The invention relates to an impeller for a pump unit, in particular for a waste-water pump unit, as well as to a pump unit with such an impeller. There are problems with contamination of the applied pump units wherever contaminated fluids are to be delivered, for example in the field of delivery of waste-water. In particular, long-fibered contamination may permanently cling to the blades of the impellers of the pump units, which leads to a compromise of the operation and even to damage of the pump unit in the extreme case. For this reason, in waste-water pumps impellers are often applied, which merely have one flow channel. With these impellers, there are no edges or walls, to which long-fibered contamination may cling. Another possibility is to design the impellers in an open manner, so that contamination may not get stuck on the blades. These designs, however, have the disadvantage that the efficiency of the pump units worsens.